Sorry, either I made a mistake or something changed quite a bit since last night when I tried this out. These are (now?) just demos.
OnLive has made 16 Independent Games Festival nominees and honorable mentions available to play for free on their service until March 11. Currently the service is UK and US only. Creating an account is free.
Among those games there are a few adventure games.
- Dear Esther
- Be Good (Don't know much about this one, but I believe it's an AG)
- Lume
- To the Moon.
The press release with full list of games is
here.